Hi,
As far as I can see, you are using low-level procedures. So, I can only suppose why the issue occurs.
The error that you obtained means that the low-level procedure refers to the window that no more exists. This error typically occurs if the tested object, window or control or its parent object was deleted or recreated during the method call or before it.
I suggest you to check whether all the initial conditions of the test run are the same as they were when you recorded this test. You can also try to re-record these low-level procedures.
I hope this helps.
Ann